Relationship between zonal distribution of microsomal cytochrome P-450s (P-45017α,lyase and P-450C21) and steroidogenic activities in guinea-pig adrenal cortex

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Abstract
In an attempt to elucidate the functional role of the three zones of the adrenal cortex, the localization of microsomal cytochrome P-450s (P-45017α,lyase and P-450C21) and their relation to steroidogenesis in the guinea-pig adrenal cortex were studied. The intracellular localization and zonal distribution of P-45017α,lyase and P-450C21 were examined by the direct peroxidase-labelled antibody technique. The cytochromes were localized immunocytochemically on the smooth-surfaced endoplasmic reticulum. P-45017α,lyase was found to be distributed in the zona fasciculata, especially in the externa, and less in the zona reticularis. The zona glomerulosa was negative for immunohistochemical staining for P-45017α,lyase. In contrast, P-450C21 was distributed in all three zones in the adrenal cortex. The cytochrome P-450 contents and their steroidogenic activities were determined with microsomes prepared from the outer zone (zonae glomerulosa and fasciculata) and from the inner zone (zona reticularis) of guinea-pig adrenals. Using an enzyme-linked immunosorbent assay, the ratio of P-450C21 content in the inner zone to that in the outer zone microsomes was estimated to be 1 ·24. 21-Hydroxylase activity was higher in the inner zone microsomes, which was in good agreement with the relative P-450C21 contents. The ratio of P-45017α,lyase content in the inner zone to that in the outer zone microsomes was estimated to be 0·75. 17α-Hydroxylase and C17–20-lyase activities were five- to sixfold greater in the outer than in the inner zone microsomes, which could not be explained by the P-45017α,lyase contents in the two zones. The effects of ACTH on the zonal distribution of microsomal cytochrome P-450s and their steroidogenic activities were also investigated. J. Endocr. (1988) 119, 191–200